DB query to use in external site

[lalaloo]

Here is the scenario i need to work on :

 

Each product has 5 units to sell. So basics of code should be :

 

If a unit is sold for this $product_id

foreach sale

show $buyer_field1

 

else show

banner_1.gif

 

Is this possible? Is there a mod? Feed? or can someone help me write the PHP code for this?

Thank you in advance